1. Field of the Invention
This invention relates generally to centrifugal pumps and relates specifically to a two-piece bearing housing for use in a centrifugal pump.
2. Description of Related Art
Centrifugal pumps generally comprise a pump casing in which an impeller is positioned to rotate for the processing of fluid material. The impeller, which is connected to a drive shaft, is part of a rotating assembly that further comprises the drive shaft, ball bearings, seals, a mechanical shaft seal and various associated hardware. The rotating assembly is bolted to the pump casing in a manner that facilitates removal of the rotating assembly for repair or replacement. Further, a bearing housing is provided to house the drive shaft, at least one set of bearings and associated seals that support and isolate the drive shaft.
A bearing housing may be comprised of two chambers, including the bearing oil chamber and the mechanical seal oil chamber. The bearing oil chamber houses bearings for the drive shaft and is separately provided with lubricating fluid for the bearings. The mechanical seal oil chamber is typically isolated from the bearing oil chamber and is provided with a separate source of lubrication to lubricate the lip seals and mechanical shaft seal about the impeller.
The bearing housing of conventional centrifugal pumps is made of a one piece casting. In certain types of bearing housings, the casting of the one-piece bearing housing is complicated by the existence of the separate bearing oil chamber and the mechanical seal oil chamber. That is, two sand cores are made corresponding to the two separate oil chambers. The two sand cores are then positioned in a larger mold corresponding to the outer housing. Molten metal is then poured into the mold and about the two sand cores to produce the casting of the bearing housing.
The manufacture of a one-piece bearing housing is made difficult by the exacting placement of the two sand cores in order to provide the separate oil chambers. Additionally, it is difficult to get the molten metal to flow into the inner walls of the mold to form the wall which separates the two chambers.
Moreover, a gas is produced by the sand core material during the casting process when the core material is contacted with the molten metal. If the gas cannot escape the mold, it forms undesirable porosities in the wall of the casting.
The porosities essentially represent leaks through the wall of the casting and can be from moderate to severe in the degree to which the porosities extend into or through the wall of the casting. The existence of the porosities result in a certain number of castings being unusable, which increases the scrap rate for the casting process. The overall cost of the castings is increased proportionally to the amount of scrap that is produced through bad castings.
A further problem encountered with the present one-piece casting of bearing housings is the fact that core sand is difficult to extract from the casting. Additionally, metal chips resulting from the machining of the casting are difficult to remove from the casting. Consequently, a great deal of time and cost is spent attempting to produce a casting that is free of residual sand and metal chips, and attempts to remove metal chips and sand from the casting may not be entirely successful.
An additional cost concern relating to conventional one-piece bearing housings is the fact that the bearing housing is made of, for example, stainless steel when the pump is going to be used for more corrosive slurry processing. As such, the bearing housing must be made entirely from stainless steel due to the casting process. Because of the unitary, or one piece casting, no cost benefit can be derived from making part of the bearing housing from another, less costly metal material.
Thus, it would be advantageous in the centrifugal pump industry to provide a bearing housing that is more easily produced and with more accuracy, thereby reducing the amount of scrap castings. It would also be advantageous to provide a bearing housing that can be made from different metals to reduce the overall cost of the casting process and thereby reduce the cost of the pump and its operation.